Temperature responsive electrical element and method



Dec. 9, 1969 s, F, GALAssO ET AL 3,483,139

TEMPERATURE RESPONSIVE ELECTRICAL ELEMENT AND METHOD Filed March 18, 1966 3 Sheets-Sheet l o O o 3 AgI CuI

INVENTORS SALVATORE F. GALASSO ROBERT B. GRAF BY MORGAN, FINNEGAN, DURHAM a PINE ATTORNEYS Dec. 9, 1969 s; F. GALASSO ET AL 3,483,139

TEMPERATURE RESPONSIVE ELECTRICAL ELEMENT AND METHOD Filed March 18, 1966 3 Sheets-Sheet 2 LLI |4o 0: LL] 0. 2 E 120- l 80 85 9o 95 IOO A93 Ausz MOL 2 3 INVENTORS SALyATQRE F. GALASSO ROBERT B. GRAF BY MORGAN, FINNEGAN, DURHAM 8 PINE ATTORNEYS Dec. 9, 1969 Filed March 18. 1966 L0 G R S. F. GALASSO ET AL 3,483,139

TEMPERATURE RESPONSIVE ELECTRICAL ELEMENT AND METHOD 5 Sheets-Sheet 3 TEMPERATURE C FIG.'3

INVENTORS SALVATORE F. GALASSO ROBERT B. GRAF BY MORGAN, FINNEGAN, DURHAM 8| PINE ATTORNEYS US. Cl. 252518.. 1 2 Claims ABSTRACT OF THE DISCLOSURE Disclosed are compositions comprised of silver and copper iodide and silver and gold sulfide which have a negative temperature coefficient of resistance, making such compositions useful as thermistors and the like.

This invention relates to electro-thermal elements particularly temperature sensitive electrical elements for use as thermistors and thermostatic switches.

At the present time there is a particular need for thermistors which exhibit large changes in electrical resistivity with small changes in temperatures. Available thermistor materials for fire detection systems are inadequate for modern usage. Commercial thermistors have coefiicients of resistivity of less than 8% per degree centigrade, while a step sensor is desired for fire detection. In addition, it has been reported that many flights are aborted because of false fire warnings which result from faulty temperature sensing systems in aircraft.

Objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the steps, methods, compositions, combinations and improvements pointed out in the appended claims.

The invention consists in the novel steps, methods, compositions, combinations and improvements herein shown and described.

An object of this invention is to provide improved electro-thermal elements, particularly temperature sensitive electrical elements for use as thermistors and thermostatic switches.

Another object of this invention is to provide improved temperature-sensitive control elements having sharply non-linear temperature resistance characteristics over certain predetermined narrow temperature ranges.

A still further object of this invention is to provide improved temperature-sensitive control elements which exhibit a marked increase in conductivity over a certain predetermined temperature range.

As is presently known, certain materials have the property of rather abruptly decreasing resistivity at a characteristic temperature. Examples of materials of the aforementioned type, and which have a negative temperature coeflicient of resistance are silver sulfide (Ag S), iron sulfide (FeS), vanadium pentoxide (V vanadium dioxide (V O vanadium trioxide (V 0 vanadium monoxide (VO), molybdenum trioxide (M00 and titanium trioxide Ti O While the materials of the above mentioned type have found useful applications where an abrupt change in resistivity is desired at a particular predetermined temperature (which is the transition temperature of the ma terial) they are not useful in electro-thermal applications where a change in resistivity is desired over a certain predetermined narrow temperature range.

Then, too, since such materials exhibit the abrupt U i d. SW68 PM) 'ice change in resistivity at a specific temperature, they do not provide a system wherein over a wide temperature range one can, by adjusting the chemical make-up thereof, obtain an electrical control composition having an abrupt change in resistivityat a predetermined or narrow temperature range within said wide temperature range. 1

In the drawings:

FIG. 1 illustrates graphically by a phase diagram an AgI and CuI solid solution system.

FIG. 2 illustrates graphically by a phase diagram an Ag AuS -Ag S solid solution system.

FIG. 3 illustrates graphically the electrical resistance change of the solid solution system of FIG. 2 wherein the composition changes from a low form composition at point A to a high form composition at point D.

It has been found that the objects of this invention may be realized by employing as compositions of electro-thermal elements, solid solution systems having a negative temperature coeflicient of resistance. Examples of solid solution systems of the aforementioned type are solid solutions containing at least one compound having a negative temperature coefficient of resistance selected from the group consisting of compounds wherein the cation is selected from the group consisting of: (a) metals of Group 1b of the Periodic Table and (b) 3-d transition metals, and wherein the anion is selected from the group consisting of oxygen, chalcogens (i.e. sulfur, tellurium and selenium) and halogens.

In forming the solid solutions used in accordance with the instant invention, the appropriate materials capable of forming a solid solution are heated to an appropriate reaction temperature wherein there is formed a solid solution; the solid solution at this elevated temperature being a one phase solid composition which may be designated the high form" solid solution. Upon cooling of the high form solid solution, the composition at an appropriate temperature range transforms into a two phase system, and upon further cooling the system reverts back into a single phase composition which may be designated the low form solid solution.

The temperature range over which the solid solution transforms from a single phase to a two phase system is the transition temperature range. It is at this transition temperature range that the solid solution system used in accordance with this invention exhibits a marked decrease in resistivity. The narrower the transition temperature range of a solid solution system, the more abrupt is the drop in resistivity. The transition temperature range for a given system depends upon the relative amounts of the components of the solid solution system.

Reference is now made to FIG. 1 of the accompanying drawing. As indicated hereinbefore, FIG. 1 is a phase diagram of an AgI and CuI solid solution system. As shown in FIG. 1 when a solid solution system formed by reacting 50 mol percent AgI and 50 mol percent CuI at a reaction temperature of 450 C., is subsequently cooled to a temperature of 250 C. there results a two phase form, one form being composition A and one form being composition B. Further heating causes composition A to change along line AC and composition B to change along line BD. At point D the mixture has completely transformed to the higher form.

When the above described solid solution is used as a temperature-responsive control element, e.g. in a thermistor, it exhibits a marked decrease in resistivity over the temperature range of 250 to 300 C., which is the transition temperature range for such solid solution system.

As shown in FIG. 2 which is a phase diagram of an A g Au s-A g s sy'stemfthe system behaves similarly to that pletely transformed to the high form.

The invention in its broader aspects is not limited to the specific steps, methods, compositions, combinations, and improvements described, but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed is:

1. A method of sensing temperature within a se1ective narrow temperature range by an abrupt change in electrical resistivity of a material at temperatures within said range comprising using as the temperature sensing element a material the composition of which consists of a solid solution of AgI and CuI having the proportions within the range of 70 mole percent to 17 mole percent UR E l of the drawings.

2. The method of clairn-i wherein the composition of the sensing element consists of an Ag S-Au S solid solution system the ratio of Ag S being from 90 mole percent to" that indicated-by the point on the ordinate underlying point C of FIGURE "2 of the drawings.

References i I UNITED STATES PATENTS I 2,740,030 3/1956 Quinn f 252518 XR OTHER REFERENCES Chemical Abstracts, vol 2 col. 2801 (1938). LEoN D. ROSDOL, Primary Examiner I. D. WELSH, Assistant Examiner 

